Portable panoramic laser mapping and/or projection system

ABSTRACT

Techniques are described herein that are capable of forming a depth map and/or projecting an image onto object(s) based on the depth map. A depth map is a three-dimensional representation of an environment. Forming the depth map may utilize a progressive resolution refinement technique. For example, locating information may be determined in accordance with the progressive resolution refinement technique in response to performing a scan of a current point over a field of view. The current point is a point, selected from a plurality of points (e.g., a grid of points) in the field of view, to which a detection beam of light is directed at a respective time as the scan is performed over the field of view. In accordance with this example, the locating information may be coordinated with the scan to form the depth map.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a division of U.S. patent application Ser. No.14/747,832, filed Jun. 23, 2015 and entitled “Portable Panoramic LaserMapping and/or Projection System,” the entirety of which is incorporatedby reference herein.

BACKGROUND

With new developments in areas such as self-driving cars, computeranimation, 3D printing, and construction, there is an ever increasingdemand for the ability to accurately map an environment (e.g., aperson's surroundings) more quickly and/or at lower cost. Lasers areoften used to map an environment. However, conventional laser mappingsystems typically measure the distance to each point in the environmentthousands of times in order to average out noise. Such repetitivemeasuring may substantially increase an amount of time that is consumedto generate a map and/or a cost associated with generating the map.Moreover, conventional laser mapping systems usually consume asubstantial amount of power (e.g., tens of watts) to measure thedistances to the points, which are used to generate a map. Therelatively high power consumption of such conventional systems mayresult in a relatively high cost. The relatively high cost and/or timeconsumption associated with conventional laser mapping systems mayrender those systems unsuitable for some applications.

SUMMARY

Various approaches are described herein for, among other things, forminga depth map and/or projecting an image onto object(s) based on the depthmap. A depth map is a three-dimensional representation of anenvironment. Forming a depth map may involve scanning a beam of laserlight from a central reference location over a grid of points within anenvironment. For example, at each point within a grid of points,locating information such as distance and velocity is measured. Duringeach measurement, the point being measured is referred to as the currentpoint. Determining distance and/or velocity from the locatinginformation at the current point may utilize a progressive resolutionrefinement (PRR) technique. In accordance with this example, thelocating information may be coordinated with the scan to form the depthmap.

An example portable panoramic laser mapping system is described. Theportable panoramic laser mapping system includes a depth measurementsubsystem, a microelectromechanical systems-based (MEMS-based) scanningsubsystem, and a controller. The depth measurement subsystem isconfigured to measure a distance between a reference location and acurrent point. The depth measurement subsystem includes a laser source,splitting optics, a light detecting structure, and a signal processingcircuit. The laser source is configured to generate coherent light. Thecoherent light is capable of being modulated. The splitting optics areconfigured to create a reference beam of light and a detection beam oflight from the coherent light. The light detecting structure isconfigured to convert the reference beam and a reflected detection beaminto electrical signals. The reflected detection beam results fromreflection of the detection beam from the current point. The signalprocessing circuit is optionally configured to determine locatinginformation based on the electrical signals in accordance with aprogressive resolution refinement technique. The locating informationindicates the distance between the reference location and the currentpoint. The MEMS-based scanning subsystem includes mirror(s) and a lightredirecting element that has a microelectromechanical structure. Themicroelectromechanical structure is configured to perform a scan of thecurrent point within a field of view using the mirror(s). The controlleris configured to coordinate the locating information with the scan ofthe current point over the field of view to form a depth map.

An example method of adapting a pixel size and/or a measurementresolution on a pixel-by-pixel basis is described. In accordance withthis method, a laser is used to generate an emission of coherent light.The emission is split into a reference beam of light and a detectionbeam of light. A scan is performed. The scan comprises a series ofdistance measurements using the detection beam as the detection beam isscanned over a line or over an area. A range of frequencies and/or aperiod of time over which the emission is modulated during the scan isaltered for a subset of the distance measurements in the scan.

In an aspect of this method, a plurality of operations may be performedfor each distance measurement in the scan. For instance, the pluralityof operations may include modulating the emission over the range offrequencies and over the period of time. The plurality of operations mayinclude orienting the detection beam toward a point on an object. Theplurality of operations may include reflecting the detection beam off ofthe point on the object to provide a reflected detection beam. Theplurality of operations may include combining the reference beam andreflected detection beam on a detector to produce an electrical signal.The electrical signal has a beat frequency. The plurality of operationsmay include signal processing the electrical signal to determine thebeat frequency. The beat frequency is a measurement of a distance to thepoint on the object.

An example method of performing progressive resolution refinement isdescribed. In accordance with this method, a first measurement with arelatively low resolution is performed using an electrically modulatedlaser source. The first measurement is processed electrically todetermine low-resolution locating information. A second measurement witha relatively high resolution is performed. The second measurement isprocessed electrically using the low-resolution locating information toenable the processing of the second measurement to determinehigh-resolution locating information.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Moreover, itis noted that the invention is not limited to the specific embodimentsdescribed in the Detailed Description and/or other sections of thisdocument. Such embodiments are presented herein for illustrativepurposes only. Additional embodiments will be apparent to personsskilled in the relevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate embodiments of the present inventionand, together with the description, further serve to explain theprinciples involved and to enable a person skilled in the relevantart(s) to make and use the disclosed technologies.

FIG. 1 is a block diagram of an example portable panoramic laser mappingand/or projection system in accordance with an embodiment describedherein.

FIG. 2 depicts an example implementation of a depth measurementsubsystem shown in FIG. 1 in accordance with an embodiment describedherein.

FIG. 2 a depicts an example implementation of a voltage-controlledoscillator (VCO) architecture in accordance with an embodiment describedherein.

FIG. 2 b depicts an example implementation of a phase-locked loop (PLL)architecture in accordance with an embodiment described herein.

FIG. 2 c depicts an example implementation of an amplitude modulatedcontinuous wave (AMCW) architecture in accordance with an embodimentdescribed herein.

FIG. 3 depicts an example implementation of a microelectromechanicalsystems-based (MEMS-based) scanning subsystem shown in FIG. 1 inaccordance with an embodiment described herein.

FIG. 4 depicts an example implementation of a microelectromechanicalstructure shown in FIG. 3 in accordance with an embodiment describedherein.

FIG. 5 depicts a flowchart of an example method for adapting a pixelsize and/or a measurement resolution on a pixel-by-pixel basis inaccordance with an embodiment described herein.

FIG. 6 depicts a flowchart of an example method for performing a scan inaccordance with an embodiment described herein.

FIGS. 7-9 depict flowcharts of example methods for performingprogressive resolution refinement in accordance with embodimentsdescribed herein.

FIG. 10 depicts a flowchart of an example method for using a depthmapping apparatus in accordance with an embodiment described herein.

FIG. 11 is a block diagram of a computing system that may be used toimplement various embodiments.

The features and advantages of the disclosed technologies will becomemore apparent from the detailed description set forth below when takenin conjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION I. Introduction

The following detailed description refers to the accompanying drawingsthat illustrate exemplary embodiments of the present invention. However,the scope of the present invention is not limited to these embodiments,but is instead defined by the appended claims. Thus, embodiments beyondthose shown in the accompanying drawings, such as modified versions ofthe illustrated embodiments, may nevertheless be encompassed by thepresent invention.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” or the like, indicate that the embodimentdescribed may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesare not necessarily referring to the same embodiment. Furthermore, whena particular feature, structure, or characteristic is described inconnection with an embodiment, it is submitted that it is within theknowledge of one skilled in the relevant art(s) to implement suchfeature, structure, or characteristic in connection with otherembodiments whether or not explicitly described.

II. Example Embodiments

Example embodiments described herein are capable of forming a depth mapand/or projecting an image onto object(s) based on the depth map. Adepth map is a graphical three-dimensional representation of anenvironment. Forming a depth map may involve scanning a beam of laserlight from a central reference location over a grid of points within anenvironment. For example, at each point within a grid of points,locating information such as distance and velocity is measured. Duringeach measurement, the point being measured is referred to as the currentpoint. Determining distance and or velocity from the locatinginformation at the current point may utilize a progressive resolutionrefinement (PRR) technique. In accordance with this example, thelocating information may be coordinated with the scan to form the depthmap.

Example techniques described herein have a variety of benefits ascompared to conventional laser mapping techniques and conventional laserprojection techniques. For instance, the example mapping techniques maybe capable of accurately mapping an environment more quickly and/or atlower cost than conventional laser mapping techniques. As anillustration, the example mapping techniques may take one or twomeasurements per point in in the environment; whereas, conventionaltechniques may take thousands of measurements per point. The examplemapping techniques may reduce an amount of time that is consumed togenerate a map and/or a cost associated with generating the map, ascompared to conventional laser mapping techniques. The example mappingtechniques may require less (e.g., substantially less) laser poweroutput than conventional laser mapping techniques. For example, theexample mapping techniques may require less than 1 Watt of laser outputpower; whereas, the conventional laser mapping techniques may requiretens of watts. In an aspect of this example, the example mappingtechniques may output less than 1 watt (W) while maintaining adetectable signal at a target distance of at least 200 m, 300 m, 400 m,or 500 m. The example projection techniques may be capable of modifyingan image that is to be projected on object(s) in the field of viewwithin a range of 0.1-10 m to compensate for variations in surface(s) ofthe object(s).

The example portable panoramic laser mapping systems described hereinmay be characterized by a relatively low manufacturing cost. Forinstance, the described portable panoramic laser mapping systems may bemade using commoditized lasers. The portable panoramic laser mappingsystems may combine a depth measurement subsystem, amicroelectromechanical systems-based (MEMS-based) scanning subsystem,and a controller into a single portable package. In an exampleimplementation, a laser projection subsystem also may be included in thesingle portable package. The depth measurement subsystem, the MEMS-basedscanning subsystem, and/or the laser projection subsystem may sharecircuitry, thereby further reducing the manufacturing cost of thedescribed portable panoramic laser mapping systems.

The example portable panoramic laser mapping systems may be usable inmore applications than conventional laser mapping systems andconventional laser projection systems. For instance, combining lasermapping functionality (e.g., mapping surroundings) and laser projectionfunctionality (e.g., projecting images overlaid on the mappedsurroundings) within a portable panoramic laser mapping system enablesthe portable panoramic laser mapping system to be used in applicationsbeyond those in which a laser mapping system or a laser projectionsystem alone may be used. For example, the device may be used in aconstruction application in which images of proposed remodeling designs,hidden facilities, or drill patterns or illumination to installequipment, such as an HVAC aperture, in a structure are overlaid onobjects (e.g., walls) inside the structure. In another example, thedevice may be used to take a relatively detailed 3D scan of a smallobject (such as a coffee mug) and print meta-information on the objector in a vicinity of the object to indicate how to order another one ormore of the object, and further optionally capture feedback from a uservia gesture or other detected motion within the device's field of view.

In order to achieve a lowest-cost design point without sacrificingperformance, the example techniques described herein may provideimprovements in multiple areas, as compared to conventional techniques.For instance, through the use of a progressive resolution refinementtechnique, the example techniques may reduce complexity and/or cost ofsignal processing, as compared to conventional techniques. Through theuse of flexural-based MEMS systems, the example techniques may achieve asubstantially lower scanning cost than conventional techniques. Theexample techniques may utilize higher-performance MEMS materials toachieve relatively wide scan angles.

FIG. 1 is a block diagram of an example portable panoramic laser mappingand/or projection system 100 (hereinafter “system 100”) in accordancewith an embodiment described herein. Generally speaking, system 100operates to perform laser mapping and/or projection. For example, system100 may perform laser mapping to form a depth map, which is athree-dimensional representation of an environment. In another example,system 100 may perform laser projection to project an image ontoobject(s) based on such a depth map. It will be recognized thatprojection (a.k.a. image projection or laser projection) as describedherein is a generalization of projecting any visible two-dimensionalinformation, including but not limited to a single still image, multiplestill images, video data, and/or partially or fully synthesized visibleinformation (e.g., augmented reality). Detail regarding techniques forperforming laser mapping and/or projection is provided in the followingdiscussion.

As shown in FIG. 1 , system 100 includes a depth measurement subsystem102, a microelectromechanical systems-based (MEMS-based) scanningsubsystem 104, a laser projection subsystem 106, a controller 108, and areference fiber optic loop 110. Depth measurement subsystem 102 isconfigured to measure a distance between a reference location 132 and acurrent point 134 in a field of view 130. For instance, depthmeasurement subsystem 102 provides a detection beam 126, which is splitfrom coherent light, to MEMS-based scanning subsystem 104 so thatMEMS-based scanning subsystem 104 may provide the detection beam 126from the reference location 132 to the current point 134. Depthmeasurement subsystem 102 receives a reflected detection beam 128, whichresults from reflection of the detection beam 126 from the current point134 at a surface of an object 112. Depth measurement subsystem 102compares a representation of the reflected detection beam 128 and arepresentation of a reference beam, which is split from the coherentlight, to determine locating information. The locating informationincludes a measurement of the distance between the reference location132 and the current point 134.

Depth measurement subsystem 102 is capable of modulating the coherentlight from which the detection beam 126 and the reference beam aresplit. For example, depth measurement subsystem 102 may modulate thecoherent light based on a modulation signal 118 that is received fromcontroller 108. In accordance with this example, the modulation signal118 may indicate a type of modulation (e.g., amplitude modulation orfrequency modulation) to be applied to the coherent light and/or amanner in which such modulation is to be applied (e.g., the amplitudesand/or frequencies to be used). Depth measurement subsystem 102 mayprovide a measurement signal 122 to controller 108. For instance, themeasurement signal 122 may include information regarding the distancebetween the reference location 132 and the current point 134.

Depth mapping using coherent light can take any of a variety of forms inamplitude and/or frequency modulation techniques. Given the superiornoise rejection capability and reduced issues with multiple reflectionscompared to amplitude modulation techniques, the discussion herein isfocused more on frequency modulation techniques. However, it will berecognized that the embodiments described herein may utilize anysuitable amplitude and/or frequency modulation techniques. Some exampletechniques for achieving Frequency Modulated Continuous Wave (FMCW)depth mapping are described in U.S. Pat. No. 4,611,912 to Falk et al.and U.S. Pat. No. 4,830,486 to Goodwin, both of which are incorporatedherein by reference in their entireties.

MEMS-based scanning subsystem 104 is configured to scan the currentpoint 134 over the field of view 130. During the scan, MEMS-basedscanning subsystem 104 provides the detection beam 126 from thereference location 132 to the current point 134, causing the reflecteddetection beam 128 to be reflected toward depth measurement subsystem102. The detection beam 126 travels a distance D before coming intocontact with object 112 at the current point 134.

Laser projection subsystem 106 is configured to project an image ontoobject(s), such as object 112, by raster scanning a beam of modulatedlaser light typically sourced from the combination of one to threevisible laser outputs. U.S. Pat. No. 8,416,482 to Desai et al., theentirety of which is incorporated herein by reference, presents such aprojection system. The combined output is referred to as visible light124. Laser projection subsystem 106 may project the image in response toreceiving a modification signal 114 from controller 108. For example,the modification signal 114 may include a modified version of the image.In another example, the modification signal 114 may include attribute(s)and/or instructions for the laser projection subsystem 106 to modify theimage prior to projection of the image onto the object(s). For instance,the image may be modified to compensate for variations in distancesbetween the reference location 132 and the surface(s) of the object(s).

Controller 108 is configured to coordinate the locating information withthe scan of the current point over the field of view 130 to form a depthmap 138. Controller 108 is shown in FIG. 1 to include a store 136 forstoring the depth map 138 for illustrative purposes and is not intendedto be limiting. It will be recognized that controller 108 need notnecessarily include a store 136.

Controller 108 may be further configured to control depth measurementsubsystem 102, MEMS-based scanning subsystem 104, and/or laserprojection subsystem 106. For instance, controller 108 may control anyone or more of the aforementioned subsystems 102, 104, and 106 based onmeasurement 122. In one example implementation, controller 114 generatesthe modification signal 114 in response to receipt of measurement 122from depth measurement subsystem 102. For example, controller 108 maygenerate the modification signal 114 to accommodate the distance betweenthe reference location 132 and the current point 134, as reflected bymeasurement 122. In another example implementation, controller 108controls MEMS-based scanning subsystem 104 using control signal 116. Forinstance, controller 108 may use the control signal 116 to control arate at which MEMS-based scanning subsystem scans the current point 134over the field of view 130. In another example implementation,controller 108 controls depth measurement subsystem 102 usingprogressive resolution refinement control signal 140. For instance,controller 108 may use the progressive resolution refinement controlsignal 140 to control the electronic signal processing of the locatinginformation associated with the current point 134.

Controller 108 may be configured to calibrate depth measurementsubsystem 102. For example, controller 108 may be configured tocalibrate depth measurement subsystem 102 using a measurement of thedistance from the reference location 132 to a reference object (e.g.,object 112) in the field of view 130. In accordance with this example,the distance from the reference location 132 to the reference object inthe field of view 130 is a known distance. For instance, the distancefrom the reference location 132 to the reference object may be knownprior to the measurement of the distance from the reference location 213to the reference object being taken.

In another example, controller 108 uses reference fiber optic loop 110to calibrate depth measurement subsystem 102. In accordance with thisexample, controller 108 calibrates depth measurement subsystem 102 usinga measurement of the distance through reference fiber optic loop 110. Infurther accordance with this example, the distance through referencefiber optic loop 110 is a known distance. For instance, the distancethrough reference fiber optic loop 110 may be known prior to themeasurement of the distance through reference fiber optic loop 110 beingtaken. The distance through reference fiber optic loop 110 may bemeasured simultaneously with the measurement of the distance from thereference location 132 to each current point 134 in the field of view130, though the scope of the example embodiments is not limited in thisrespect.

Controller 108 may calibrate depth measurement subsystem 102 once per Nmeasurements of the current point 134 in the field of view 130, N timesper linear scan of the current point 134 in the field of view 130, Ntimes per scan of the entire field of view 130, once per N scans of theentire field of view 130, etc. N is an integer (e.g., a predeterminedinteger), such as 1, 2, 3, 4, or 5.

In an example embodiment, controller 108 utilizes the depth map 138 toprovide a modified image. In accordance with this embodiment, laserprojection subsystem 106 is configured to generate the visible light 124for projecting the modified image onto object(s), such as the object112. In an aspect of this embodiment, laser projection subsystem 106 mayuse a light redirecting element in MEMS-based scanning subsystem 104that is configured to perform the scan of the current point 134 over thefield of view 130 to project the modified image onto the object(s). Inanother aspect of this embodiment, MEMS-based scanning subsystem 104 mayfurther include a second light redirecting element, which is differentfrom the light redirecting element configured to perform the scan of thecurrent point 134 over the field of view 130. In accordance this thisaspect, laser projection subsystem 106 uses the second light redirectingelement in MEMS-based scanning subsystem 104 to project the modifiedimage onto the object(s).

Controller 108 may be configured to determine velocity of at least onepoint in the field of view 130 based on the locating information. Forexample, controller 108 may be configured to determine a gesture basedon velocities of at least two points in the field of view 130. In anaspect of this example, controller 108 may determine the gesture basedon a relative velocity between the at least two points. Examples of agesture include but are not limited to a hand being waved and a fingerbeing pointed. Controller 108 may be configured to determine that anobject is moving relative to the system 100 and/or a rate at and/or adirection in which an object is moving relative to system 100.

It will be recognized that system 100 may not include one or more ofdepth measurement subsystem 102, MEMS-based scanning subsystem 104,laser projection subsystem 106, controller 108, and/or reference fiberoptic loop 110. Furthermore, system 100 may include components inaddition to or in lieu of depth measurement subsystem 102, MEMS-basedscanning subsystem 104, laser projection subsystem 106, controller 108,and/or reference fiber optic loop 110.

FIG. 2 is a block diagram of an example depth measurement subsystem 200in accordance with an embodiment described herein. Depth measurementsubsystem 200 is an example implementation of a depth measurementsubsystem 102 shown in FIG. 1 . Depth measurement subsystem 200 includesa laser source 202, splitting optics 204, a light detecting structure206, progressive resolution refinement (PRR) circuitry 220, and a signalprocessing circuit 210.

Laser source 202 is configured to generate coherent light 244. Forinstance, the coherent light 244 may be an infrared laser with emissionwavelengths between 800 nm-2000 nm. In accordance with this example, theinfrared laser may have a wavelength of 850 nanometers (nm), 940 nm,1310 nm, 1550 nm, or any other suitable value. For instance, wavelengthsfrom 1300 to 2000 nm may provide reduced absorption and scattering fromdust. The output power of laser source 202 may be less than 100milliwatts (mW) for mapping regions of 10 m or less. For regions inexcess of 10 m, higher powers may be needed to achieve sufficiently highreflected signals for determining locating information.

Laser source 202 is capable of modulating the coherent light 244. Forinstance, laser source 202 may modulate the coherent light 244 infrequency and/or amplitude. Laser source 202 may modulate the coherentlight 244 in response to (e.g., based on) receipt of the modulationsignal 118, though the scope of the example embodiments is not limitedin this respect. By modulating a current supply to laser source 202, thewavelengths of the coherent light 244 can be swept anywhere fromthousandths of a nanometer to multiple nanometers. The sweep inwavelength can produce large changes in the optical emission frequency.As an example, tenths of a nanometer corresponds to several gigahertz(GHz) changes in optical emission frequency.

In the case of frequency modulation, the modulation signal 118 may beswept over a linear saw-tooth profile with a period in a range of 5nanoseconds (ns) to 500 milliseconds (ms). Frequency modulation changesin a range of 150 MHz to 150 GHz may be utilized depending on the speedand range resolution that are needed.

There are many ways to modulate amplitude and/or frequency of a laser'semission. For that reason, we refer to the combination of the laser andthe modulator as the laser source 202 herein for the purpose ofdiscussion. An example for frequency modulation would be a distributedfeedback laser (DFB) diode laser powered by a current source. Bylinearly ramping the current source output in time, the frequency of thelaser's emission can be linearly modulated. Varying the temperature of adiode laser is yet another way to modulate a diode laser's emissionfrequency, though it may not be well suited for the time constantsassociated with depth mapping. An example for amplitude modulation wouldbe a diode laser followed by an optical chopper.

Splitting optics 204 are configured to create a reference beam 246 oflight and the detection beam 126 of light from the coherent light 244.For instance, splitting optics 204 may collimate and optically split thecoherent light 244 to create the reference beam 246 and the detectionbeam 126. Accordingly, splitting optics 204 may include collimationoptics, a splitter to split the coherent light 244, and one or morepolarizing filters for altering the detection beam 126 and/or thereference beam 246 for proper interaction between the reflecteddetection beam 128 and the reference beam 246 at a surface of lightdetecting structure 206.

Light detecting structure 206 is configured to convert the referencebeam 246 and the reflected detection beam 128 into electrical signals.The reflected detection beam 128 results from reflection of thedetection beam 126 from the current point 134, as shown in FIG. 1 . Theelectrical signals may include a beat signal 248. For instance, when thereference beam 246 and the reflected detection beam 128 combine at lightdetecting structure 206, the beat signal 248 is produced. The beatsignal 248 is an electrical result of optical mixing of the referencebeam 246 and the reflected detection beam 128 at a surface of lightdetecting structure 206.

In an example embodiment, depth measurement subsystem 200 is configuredto perform Frequency Modulated Continuous Wave (FMCW) depth mapping witha linear ramp in frequency over an interval Δf, referred to as a chirpfrequency excursion. In accordance with this embodiment, the beat signal248 has a beat frequency, which represents a measurement of the distancebetween the reference location 132 and the current point 134. The beatfrequency is directly proportional to the distance D traveled by thedetection beam 126, as shown in FIG. 1 , in accordance with thefollowing equation:

$\begin{matrix}{f_{beat} = {2( \frac{D*\Delta\; f}{c*T} )}} & ( {{Equation}\mspace{14mu} 1} )\end{matrix}$where D is the distance from the reference location 132 to the currentpoint 134; c is the speed of light; and T is the duration of the linearfrequency ramp (i.e., “chirp period”).

FMCW signals facilitate the determination of both the distance betweenthe reference location 132 and each current point 134 in the field ofview 130, and the speed of a point in the field of view 130 as it movesrelative to the reference location 132 due to the Doppler effect. Tocarry out both distance and speed measurements, a saw-tooth profile withrising and falling linear ramps in frequency may be used. Two beatfrequencies may be created whose average and difference can be used tocompute both relative speed (e.g., velocity) of an object (e.g., object112) and distance to the object. FMCW allows ranging with resolutionproportional to the bandwidth (Δf/ΔT) within the pulse window, allowingrange to be determined with a single pulse per point in the field ofview 130.

Light detecting structure 206 may be configured in many ways. Forexample, light detecting structure 206 may be mounted adjacent toMEMS-based scanning subsystem 104 and may receive light from the fieldof view 130. In another example, light detecting structure 206 may bepositioned in the optical path of splitting optics 204 and may receiveonly light from the field of view 14 that passes back through MEMS-basedscanning subsystem 104. In yet another example, light detectingstructure 206 may be integrated onto MEMS-based scanning subsystem 104as part of a composite mirror system through a layer transfer process.In accordance with this example, the medium of light detecting structure206, which may be specially designed, may be bonded to MEMS-basedscanning subsystem 104 for both mechanical and electrical connection.

Light detecting structure 206 may be made out of any of a variety oftypes of devices, depending on the application and the wavelengths ofthe coherent light 244 being used for depth measurement. Example devicesthat may be used to make light detecting structure 206 include but arenot limited to an avalanche photodiode, a Metal-Semiconductor-MetalSchottky photodiode, a photoconductive switch, and an ultra-fast p-i-nphotodiode.

Equation 1 reveals the proportional relationship between the chirpfrequency excursion and the beat frequency. As an example, consider thecase of a 10 m distance, a 20 GHz chip range, and a chirp duration of 1microseconds (μs). This set of conditions would produce a 1.33 GHz beatfrequency. Although it is possible to measure such a frequency,electronics used to process signals below 500 MHz typically are muchless expensive. To reduce the signal processing requirements, one couldreduce the chirp frequency excursion to 2 GHz; however, there is aresulting penalty in range resolution according the following equation:

$\begin{matrix}{{\delta R} = \frac{c}{2*\Delta\; f}} & ( {{Equation}\mspace{14mu} 2} )\end{matrix}$where δR is the range resolution; Δf is the chirp frequency excursion;and c is the speed of light. It can be seen from Equation 2 that a10×reduction in chirp frequency excursion results in a 10×increase inthe minimum range resolution. If in the example above, the chirpfrequency excursion were decreased to 2 GHz, the resulting beatfrequency would be decreased to 133 MHz; however, the range resolutionwould be negatively impacted by a factor of 10. The progressiveresolution refinement technique was designed to achieve the higher rangeresolution depth maps, but at a substantially lower cost and/orcomplexity of system 100.

A progressive resolution refinement technique is a technique in which afirst (e.g., relatively lower-resolution) measurement is determined, anda second (e.g., relatively higher-resolution) measurement is determinedutilizing the first measurement. By utilizing the first measurement toperform the second measurement, the cost and/or complexity of system 100may be substantially lowered.

For example, in one embodiment of progressive resolution refinement, afirst measurement may be performed where modulation signal 118 modulateslaser source 202 to produce a 2 GHz chirp frequency excursion, which asshown in the prior example, results in a beat signal 248 having a 133MHz beat frequency for an example current point with a 10 m distancefrom the reference location 132. Processing of the locating informationfrom the beat signal 248 starts with progressive resolution refinementblock 220 shown in FIG. 2 , and detailed in FIG. 2 a . Referring to FIG.2 a , for the first measurement, switch 261 would be opened and switch262 would be closed in order to bypass high frequency signal mixer 240and feed directly into signal processing circuit 210. Signal processingcircuit 210 may include element 241, which includes an analog-to-digitalconversion circuit coupled with a digital-signal-processing (i.e., DSP)block that carries out a fast Fourier transform (i.e., FFT), todetermine the value of the beat frequency in the beat signal 248. Inanother embodiment, signal processing circuit 210 may include aphased-locked loop (i.e., PLL) circuit 242 to determine a measure of thebeat frequency in the beat signal 248, a measure being the voltagerequired to lock the phased locked-loop's internal voltage controlledoscillator on the beat frequency. It will be recognized that depthmeasurement subsystem 200 need not necessarily include element 241and/or PLL circuit 242.

A second measurement using the progressive resolution refinementtechnique may be performed where modulation signal 118 modulates lasersource 202 to produce a 20 GHz chirp frequency excursion, which as shownin the prior example, results in a beat signal 248 having a 1.33 GHzbeat frequency for an example current point with a 10 m distance fromthe reference location 132. In this second measurement, switch 261 wouldbe closed and switch 262 would be opened in order to send the beatsignal with the higher beat frequency through high frequency signalmixer 240. Based on the results of the first measurement, controller 108may send progressive resolution refinement control signal 140 to selecta voltage-controlled oscillator (VCO) signal 263 from a VCO clock tree264. When VCO signal 263 is mixed with beat signal 248 using highfrequency signal mixer 240, low frequency beat signal 250 results. Lowpass filter (i.e. LPF) 290 is used to filter out other signal productsof signal mixer 240 not related to the low frequency beat signal 250.Low frequency beat signal 250 has a beat difference frequency equal tothe difference between the frequency of the VCO signal 263 and the beatfrequency of the beat signal 248. Beat difference frequency of lowfrequency beat signal 250 is a measure of the distance to the currentpoint 134. Signal processing circuit 210 may be used to constructmeasurement 122 from the beat difference frequency of low frequency beatsignal 250. For example, signal processing circuit 210 may use theaforementioned PLL or FFT circuits to determine the value of the beatdifference frequency of low frequency beat signal 250.

VCO clock tree 264 may include a progression of VCO clock signals,wherein the difference in frequency between any two successive VCO clocksignals are within the signal processing capabilities of signalprocessing circuitry 210. Based on the results of the first measurement,controller 108 may have sufficient information to predict the expectedbeat frequency of beat signal 250 during the second measurement andthereby select the appropriate VCO clock signal 263 to produce lowfrequency beat signal 250 that is within the signal processingcapabilities of signal processing circuitry 210.

The same process may be used for all the other pixels within the fieldof view. For example, the locating information for each pixel may bedetermined in a first (e.g., relatively lower-resolution) measurement tobin the approximate distance for each pixel and then using theapproximate distance from the first measurement, perform a second (e.g.,relatively high-resolution) measurement to obtain more accurate and/orprecise locating information.

In another embodiment of progressive resolution refinement, the phasedlocked loop architecture 270 shown in FIG. 2 b is used. Referring toFIG. 2 b , in order to determine locating information from the beatsignal 248, the beat signal 248 is fed into a PLL circuit 271.Controller 108 may send progressive resolution refinement control signal140 to PLL circuit 271 in order to set the center frequency of thephased locked loop such that the PLL circuit 271 can lock on the beatfrequency of the beat signal 248. Without high expense or complexity,for a single fixed center frequency, it is unlikely that PLL circuit 271could be designed to span relatively high and relatively low resolutionmeasurements over ranges of 50 m, 100 m, 200 m, 300 m, 400 m, or 500 m.In such examples, beat frequencies may need to be measureable from 10MHz to 50 GHz. High frequency PLL circuits exist, but the range offrequencies over which the PLL can rapidly lock is typically limited. Inan example embodiment of progressive resolution refinement, the phasedlocked loop architecture 270 does not need to span the entire range.

For example, a first measurement may be performed with a relatively lowresolution where the modulation signal 118 modulates laser source 202 toproduce a 2 GHz chirp frequency excursion, which as shown before,results in a beat signal 248 having a 133 MHz beat frequency for anexample current point with a 10 m distance from the reference location132. Processing of the locating information from the beat signal 248starts with the progressive resolution refinement block 220 detailed inFIG. 2 b . For the first measurement, controller 108 may provide aprogressive resolution refinement control signal 140 to PLL circuit 271to set a low center frequency thereby enabling PLL circuit 271 to lockonto relatively low beat frequency of the beat signal 248. Signalprocessing circuit 210 may include an analog-to-digital conversioncircuit to measure the control voltage for the voltage controlledoscillator within PLL circuit 271, the control voltage being a measureof the beat frequency of the beat signal 248. Furthermore, the beatfrequency provides a measure of the distance to the current point 134.

A second measurement using the progressive resolution refinementtechnique may be performed where modulation signal 118 modulates lasersource 202 to produce a 20 GHz chirp frequency excursion, which as shownin the prior example, results in a beat signal 248 having a 1.33 GHzbeat frequency for an example current point with a 10 m distance fromthe reference location 132. Based on the results of the firstmeasurement, controller 108 may have sufficient information to predictthe expected beat frequency of the low frequency beat signal 250 duringthe second measurement and thereby select the appropriate PLL centerfrequency for PLL circuit 271 to enable it to lock on to the beatfrequency of the beat signal 248. Controller 108 may set the appropriatePLL center frequency for PLL circuit 271 using the progressiveresolution refinement control signal 140. Signal processing circuit 210may include an analog-to-digital conversion circuit to measure thecontrol voltage for the voltage controlled oscillator within PLL circuit271, the control voltage being a measure of the beat frequency of thebeat signal 248. Signal processing circuit 210 may be used to constructmeasurement 122 from the measure of the beat frequency of the beatsignal 248.

It will be recognized that depth measurement subsystem 200 need notnecessarily include VCO clock tree 264, signal mixer 240, and/or phasedlocked loop architecture 270 to enable the progressive resolutionrefinement technique. Other circuit topologies to accomplish themeasurement task are possible and known to those skilled in the art ofcircuit design. Furthermore, the first measurement need not be ameasurement of the current point 134. Instead, the first measurement maybe an estimate of the distance from the reference location 132 to thecurrent point 134 based on measurements of one or more other pointswithin the field of view (e.g., another point that is adjacent to thecurrent point 134).

In an example progressive resolution refinement technique embodiment,the first measurement of the distance between the reference location 132and the current point 134 is used to narrow a frequency range over whichthe beat frequency is to be searched in the second measurement by morethan a factor of two. For example, in one embodiment, if a relativelyhigh resolution second measurement produces a beat frequency of a beatsignal 248 of 2.5 GHz, VCO architecture 259 shown in FIG. 2 a mayproduce a low frequency beat signal 250 with a difference beat frequencyof 500 MHz, 500 MHz being more than a factor of two reduction from theoriginal 2.5 GHz beat frequency. In another embodiment, for example, ifa relatively high resolution second measurement produces a beatfrequency of a beat signal 248 of 2.5 GHz, PLL circuit 271 shown in FIG.2 b may be controlled by progressive resolution refinement signal 140 tohave a center frequency near 2.5 GHz. Furthermore, PLL circuit 271 mayhave a frequency lock range of 500 MHz, 500 MHz being a range offrequencies more than a factor of two reduction from the original 2.5GHz beat frequency.

In an aspect of this embodiment, laser source 202 shown in FIG. 2 isconfigured to perform a periodic chirp in which the coherent light 244is modulated (e.g., linearly) in frequency over a chirp period of timeand over a chirp frequency excursion. In accordance with this aspect,controller 108 may be configured to adjust the chirp frequency excursionto adapt resolution of the locating information. Controller 108 may beconfigured to adapt the resolution for a single point within a scan, asubset of the points within a scan, or all of the points within a scan.

In one example of this implementation, the current point 134 has a pixelsize, which is a distance over which the current point 134 scans duringthe chirp period. In the MEMS-based scanning subsystem 104 describedabove with reference to FIG. 1 , one or more of the axes may be drivenat mechanical resonance. Accordingly, if a constant chirp period wereused, the effective pixel size may vary throughout the scan due to thesinusoidal motion of the microelectromechanical structure therein. Onetechnique for rectifying this issue is to adapt the chirp period to theangular velocity of the microelectromechanical structure to maintain aconstant pixel size or a specified pixel size. According to Equation 1,as a secondary result, the beat frequency of the beat signal 240 will bemodified as the chirp period is modified. In accordance with thistechnique, the progressive range resolution circuitry in VCOarchitecture 259 shown in FIG. 2 a could accommodate this chirp periodmodification by stretching or compressing the base VCO within the VCOclock tree 264. In doing so, each VCO signal 263 selected wouldaccommodate a constant range of distances despite varying chirp periods.

Other frequency modulation schemes may be used, in addition to or inlieu of the FMCW scheme described above. For instance, AmplitudeModulated Continuous Wave (AMCW) is another scheme in which lasermodulation can be utilized to determine both the relative speed of anobject and distance to the object.

In AMCW, one or more simultaneous carrier signals in the form offundamental sinusoidal modulation or pulse trains are emitted by lasersource 202. The modulation frequencies are chosen based on anunambiguous range to the object. Multiple frequencies of varyingamplitude ratios may be emitted either simultaneously or in a predefinedsequence to facilitate enhanced range resolution and determination ofrelative reflectivity of surfaces of the object.

In an embodiment of the AMCW technique, in accordance with theprogressive resolution refinement technique, for a first measurement ofeach point in the entire field of view 130, each point may first bescanned using a modulation frequency chosen as the maximum frequency forthe maximum unambiguous range for which the system is configured tooperate. Locating information from this first measurement willnecessarily be of lower resolution; however, using the locatinginformation from the first measurement, a second measurement may employdifferent modulation frequencies either emitted simultaneously or in apredefined sequence to obtain a relatively higher resolutionmeasurement.

In both the first measurement and the second measurement, the distanceto a given point in the field of view 130 may be given by theinstantaneous phase angle of a demodulated representation of thereflected detection beam. Demodulation and determination of theinstantaneous phase angle may be accomplished through digital signalprocessing or through analog homodyne mixing in an I/Q detector.

For example, FIG. 2 c shows an AMCW architecture 259 in accordance withthe progressive resolution refinement technique. As shown in FIG. 2 c ,multiple changes to system 100 are made to accommodate AMCW compared toFMCW, including but not limited to reference beam 248 becomes referencesignal 248A, which is an electrical representation of the amplitudemodulation signal; only reflected detection beam 128 impinges upon lightdetecting structure 206; and beat signal 248 becomes amplitude signal248B.

Internal to the AMCW architecture 259 is an I/Q detector. Referencesignal 248A provides the reference for multipliers 282 and 283. Aftermultipliers 282 and 283, low pass filter (i.e. LPF) 292 and LPF 293 passthe low frequency phase information. On one leg of the I/Q detector,phase delay 281 is used to provide the quadrature signal reference tomultiplier 282. Analog-to-digital converter (i.e., ADC) 284 and ADC 285digitize the analog signals and provide Q-Data 286 and I-Data 287,respectively. From Q-Data 286 and I-Data 287, digital signal processor(DSP) 288 is able to compute the relative phase between the referencesignal 248A and the reflected detection beam 128, the relative phasebeing a measure of the distance to the current point 134. DSP 288utilizes the first measurement and the second measurement in order todetermine the relatively high-resolution locating information containedwithin measurement 122.

AMCW architecture 259 is shown to include an I/Q detector forillustrative purposes and is not intended to be limiting. It will berecognized that there are a variety of techniques for determining thephase of an AMCW signal.

FIG. 3 is a block diagram of an example microelectromechanicalsystems-based (MEMS-based) scanning subsystem 300 in accordance with anembodiment described herein. MEMS-based scanning subsystem 300 is anexample implementation of a MEMS-based scanning subsystem 104 shown inFIG. 1 . MEMS-based scanning subsystem 300 includes a light redirectingelement 302 and mirror(s) 304. Light redirecting element 302 has amicroelectromechanical structure 306 that is configured to perform ascan 352 of the current point 134 over the field of view 130 using themirror(s) 304. For instance, microelectromechanical structure 306 mayperform the scan 352 in response to receipt of the control signal 116.Mirror(s) are configured to reflect the detection beam 126 from thereference location 132 to the current point 134 during the scan 352.

The visible light 124 may define an image that is to be projected ontoobject(s). Microelectromechanical structure 306 may be configured toproject the visible light 124 onto the object(s) using the mirror(s)304. For instance, microelectromechanical structure 306 may project thevisible light 124 onto the object(s) in response to receipt of thecontrol signal 116.

In the presence of moving objects, a Doppler shift may induce afrequency shift in the beat signal that is ambiguous with rangedetermination in the case of a linearly increasing chirp. Rising andfalling chirps may be used to cause respective beat frequencies, whichmay be used to compute both velocity and depth of points in the field ofview 130. The average of the beat frequencies represents the distance Dbetween the reference location 132 and the current pixel 134, and thedifference between the beat frequencies represents the relative velocitybetween the points.

FIG. 4 is a block diagram of an example microelectromechanical structure400 in accordance with an embodiment described herein.Microelectromechanical structure 400 is an example implementation of amicroelectromechanical structure 306 shown in FIG. 3 in accordance withan embodiment. Microelectromechanical structure 400 includes a frame402, a first inner flexure 404 a, a second inner flexure 404 b, a firstouter flexure 406 a, a second outer flexure 406 b, a first frame sensingelectrode 408 a, a second frame sensing electrode 408 b, a first mirrorsensing electrode 410 a, a second mirror sensing electrode 410 b, andmirror(s) 412.

Frame 402 provides structural support for inner flexures 404 a-404 b andmirror(s) 412.

Inner flexures 404 a-404 b and outer flexures 406 a-406 b are configuredto mount mirror(s) 412. For instance, inner flexures 404 a-404 b areshown to directly mount mirror(s) 412 via direct contact with mirror(s)412, and outer flexures 406 a-406 b are shown to indirectly mountmirror(s) 412 via indirect contact with mirror(s) 412, though the scopeof the example embodiments is not limited in this respect. Innerflexures 404 a-404 b mechanically couple frame 402 to mirror(s) 412.Inner flexures 404 a-404 b enable mirror(s) 412 to rotate about axis414, as depicted by arrow 420. Outer flexures 406 a-406 b mechanicallycouple frame 402 to a substrate 422. Outer flexures 406 a-406 b enableframe 402 to rotate about axis 416, as depicted by arrow 418.

Mirror(s) 412 is configured to reflect light (e.g., coherent light) thatis incident on mirror(s) 412. The direction in which the light isreflected is based on an extent to which mirror(s) 412 is rotated aboutaxis 414 and an extent to which flame 402 is rotated about axis 416.

Frame sensing electrodes 408 a-408 b are configured to sense motion offrame 402. For instance, frame sensing electrodes 408 a-408 b may beconfigured to sense an extent to which frame 402 rotates clockwise orcounterclockwise about the axis 416.

Mirror sensing electrodes 410 a-410 b are configured to sense motion ofmirror(s) 412. For instance, mirror sensing electrodes 410 a-410 b maybe configured to sense an extent to which mirror(s) 412 are rotatedclockwise or counterclockwise about the axis 414.

In an example embodiment, inner flexures 404 a-404 b and outer flexures406 a-406 b are used in lieu of spinning elements to mount mirror(s)412. Accordingly, microelectromechanical structure 400 may not includespinning elements.

In another example embodiment, inner flexures 404 a-404 b and/or outerflexures 406 a-406 b are formed from one or more materials having afracture toughness of at least 15 MPa(m{circumflex over ( )}½) and aYoung's modulus of at least 10 Gpa. MPa represents megapascals; GParepresents gigapascals; and m represents meters.

In yet another example embodiment, inner flexures 404 a-404 b and/orouter flexures 406 a-406 b are formed from one or more materials capableof undergoing a strain of two percent without failure.

In still another example embodiment, mirror(s) 412 are formed on asubstrate material that is different from a material from which innerflexures 404 a-404 b and/or outer flexures 406 a-406 b are formed.

In yet another example embodiment, microelectromechanical structure 400is configured to pivot at least one mirror (e.g., at least one ofmirror(s) 412) about one or more axes (e.g., axis 414 and/or axis 416)over an optical field of view greater than a threshold angle. Forinstance, the threshold angle may be 60 degrees, 70 degrees, 80 degrees,or 90 degrees.

In still another example embodiment, microelectromechanical structure400 is configured to pivot at least one mirror (e.g., at least one ofmirror(s) 412) about one or more axes (e.g., axis 414 and/or axis 416)at a frequency greater than a threshold frequency. For instance, thethreshold frequency may be 400 Hz, 500 Hz, 600 Hz, 800 Hz, or 1 kHz.

Microelectromechanical structure 400 may be configured using a 2-axismirror system, as shown in FIG. 4 , or using a pair of single axismirrors. Selection of the appropriate configuration is based on theapplication requirements. A 2-axis system may be lower in cost given thereduced assembly requirements; however, a pair of single-axis mirrorsmay be desirable for a higher performance system given the mirror sizeand drive frequency requirements.

Microelectromechanical structure 400 may be made from silicon (as aremost MEMS structures). However, depending on the applicationrequirements which may include large mirrors, higher scan frequencies,and relatively large fields-of-view, higher performance materials suchas alloyed titanium may be used in addition to or in lieu of silicon. Inone example, if a titanium alloy is used to make inner flexures 404a-404 b and/or outer flexures 406 a-406 b, the same sheet of materialmay be used for forming mirror(s) 412. Such material may be polished andcoated with a second material to increase reflectivity. In anotherexample, if the application's mirror flatness requirements arerelatively high, mirror 412 may be formed on a different substrate thaninner flexures 404 a-404 b and outer flexures 406 a-406 b and laterbonded to inner flexures 404 a-404 b. One example would be a metalcoated piece of silicon bonded to the titanium alloy using a eutecticbond.

A field-of-view of 60 degrees implies a peak-to-peak mechanicaldeflection of 30 degrees. Given the reflection off of a mirrorsubstrate, the optical field of view is twice the mechanical deflection.Peak deflections of greater than 15 degrees are formidable to achieveusing MEMS, especially as the frequency requirements exceed 1 kHz.

Actuation of microelectromechanical structure 400 could take many formsincluding electrostatic, Lorentz, or piezoelectric based forcing. For a2-axis microelectromechanical structure fabricated from silicon,electrostatic actuation may be used given the ease of fabrication,though the scope of the example embodiments is not limited in thisrespect. U.S. Pat. No. 6,753,638 to Adams et al., the entirety of whichis incorporated herein by reference, presents such a 2-axiselectrostatically actuated mirror system.

The same actuators that were used to drive microelectromechanicalstructure 400 may be used for sensing the motion ofmicroelectromechanical structure 400. For instance, frame sensingelectrodes 408 a and 408 b and/or mirror sensing electrodes 410 a and410 b may be used. Frame sensing electrodes 408 a and 408 b may bemounted to the floor below frame 402. Assuming frame 402 is made of aconductive material, a carrier signal of approximately 100 kHz and 1volt peak may be applied to frame 402. Frame sensing electrodes 408 aand 408 b may be connected to a differential input trans-impedanceamplifier and demodulation circuitry, which are known in the MEMSindustry, for sensing the motion of frame 402.

Other example techniques for sensing the motion include optical,Lorentz, piezoelectric, and capacitance-based techniques. For instance,capacitance-based techniques may be relatively simple and have arelatively lower temperature dependence than some other techniques.

FIG. 5 depicts a flowchart 500 of an example method for adapting a pixelsize and/or a measurement resolution on a pixel-by-pixel basis inaccordance with an embodiment described herein. For illustrativepurposes, flowchart 500 is described with respect to system 100 shown inFIG. 1 and depth measurement subsystem 200 shown in FIG. 2 . Furtherstructural and operational embodiments will be apparent to personsskilled in the relevant art(s) based on the discussion regardingflowchart 500.

As shown in FIG. 5 , the method of flowchart 500 begins at step 502. Instep 502, a laser is used to generate an emission of coherent light. Inan example implementation, laser source 202 uses a laser to generate anemission of coherent light 244.

At step 504, the emission is split into a reference beam of light and adetection beam of light. In an example implementation, splitting optics204 split the emission into a reference beam 246 of light and adetection beam 126 of light.

At step 506, a scan is performed. The scan comprises a series ofdistance measurements using the detection beam as the detection beam isscanned over a line or over an area. In an example implementation,MEMS-based scanning subsystem 104 performs the scan. In accordance withthis implementation, the scan comprises a series of distancemeasurements using the detection beam 126 as the detection beam 126 isscanned over a line or over an area.

At step 508, a range of frequencies and/or a period of time over whichthe emission is modulated during the scan are altered for a subset ofthe distance measurements in the scan. In an example implementation,laser source 202 alters the range of frequencies and/or the period oftime over which the emission is modulated during the scan for the subsetof the distance measurements in the scan.

In accordance with the embodiment of FIG. 5 , the pixel size is adistance over which the detection beam is scanned during a measurement.

In some example embodiments, one or more steps 502, 504, 506, and/or 508of flowchart 500 may not be performed. Moreover, steps in addition to orin lieu of steps 502, 504, 506, and/or 508 may be performed. Forinstance, in an example embodiment, the method of flowchart 500 furtherincludes altering the period of time to obtain a specified pixel size ateach measurement in a scan. In an aspect of this embodiment, thespecified pixel size is a constant pixel size over an entirety of thescan. In an implementation of this aspect, altering the period of timeto obtain the specified pixel size at each measurement comprisesaltering a primary clock of a VCO clock tree within a VCO architectureto enable the signal processing architecture to track a change in thepixel size at each measurement.

In another example embodiment, the method of flowchart 500 furtherincludes altering the range of frequencies to obtain a specifiedmeasurement resolution at each measurement in a scan.

FIG. 6 depicts a flowchart 600 of an example method for performing ascan in accordance with an embodiment described herein. Flowchart 600 isdescribed as an example implementation of step 506 shown in FIG. 5 forpurposes of illustration. For instance, the steps of flowchart 600 maybe performed for each distance measurement in the scan. For illustrativepurposes, flowchart 600 is described with respect to system 100 shown inFIG. 1 and depth measurement subsystem 200 shown in FIG. 2 . Furtherstructural and operational embodiments will be apparent to personsskilled in the relevant art(s) based on the discussion regardingflowchart 600.

As shown in FIG. 6 , the method of flowchart 600 begins at step 602. Instep 602, the emission is modulated over the range of frequencies andover the period of time. In an example implementation, laser source 202modulates the emission over the range of frequencies and over the periodof time.

At step 604, the detection beam is oriented toward a point on an object.In an example implementation, MEMS-based scanning subsystem 104 orientsthe detection beam 126 toward a current point 134 on an object 112.

At step 606, the detection beam is reflected off of the point on theobject to provide a reflected detection beam. In an exampleimplementation, MEMS-based scanning subsystem 104 reflects the detectionbeam 126 off of the current point 134 on the object 112 to provide areflected detection beam 128.

At step 608, the reference beam and reflected detection beam arecombined on a detector to produce an electrical signal. The electricalsignal has a beat frequency. In an example implementation, lightdetecting structure 206 combines the reference beam 246 and thereflected detection beam 128 thereon to produce beat signal 248. Inaccordance with this implementation, the beat signal 248 has the beatfrequency.

At step 610, the electrical signal is signal processed to determine thebeat frequency. The beat frequency is a measurement of a distance to thepoint on the object. In an example implementation, signal processingcircuit 210 signal processes the beat signal 248 to determine the beatfrequency. In accordance with this implementation, the beat frequency isa measurement of a distance to the current point 134 on the object 112.

In some example embodiments, one or more steps 602, 604, 606, 608,and/or 610 of flowchart 600 may not be performed. Moreover, steps inaddition to or in lieu of steps 602, 604, 606, 608, and/or 610 may beperformed.

FIGS. 7-9 depict flowcharts 700 and 800 of example methods forperforming progressive resolution refinement in accordance withembodiments described herein. FIG. 10 depicts a flowchart 1000 of anexample method for using a depth mapping apparatus in accordance with anembodiment described herein. For illustrative purposes, flowcharts 700,800, 900, and 1000 are described with respect to system 100 shown inFIG. 1 and depth measurement subsystem 200 shown in FIG. 2 . Furtherstructural and operational embodiments will be apparent to personsskilled in the relevant art(s) based on the discussion regardingflowcharts 700, 800, 900, and 1000.

As shown in FIG. 7 , the method of flowchart 700 begins at step 702. Instep 702, a first measurement with a relatively low resolution isperformed using modulated coherent light. In an example implementation,depth measurement subsystem 102 performs the first measurement with therelatively low resolution using the modulated coherent light.

At step 704, the first measurement is processed electrically todetermine low-resolution locating information. The low-resolutionlocating information includes a relatively low resolution estimate of adistance between a reference location and a current point. In an exampleimplementation, signal processing circuit 210 processes the firstmeasurement electrically to determine the low-resolution locatinginformation. In accordance with this embodiment, the low-resolutionlocating information includes a relatively low resolution estimate ofthe distance between the reference location 132 and the current point134.

At step 706, a second measurement with a relatively high resolution isperformed. In an example implementation, depth measurement subsystem 102performs the second measurement with the relatively high resolution.

At step 708, the second measurement is processed electrically using thelow-resolution locating information to enable the processing of thesecond measurement to determine high-resolution locating information.The high-resolution locating information includes a relatively highresolution estimate of the distance between the reference location andthe current point. In an example implementation, signal processingcircuit 210 processes the second measurement electrically using thelow-resolution locating information to enable the processing of thesecond measurement to determine the high-resolution locatinginformation. In accordance with this implementation, the high-resolutionlocating information includes a relatively high resolution estimate ofthe distance between the reference location 132 and the current point134.

In some example embodiments, one or more steps 702, 704, 706, and/or 708of flowchart 700 may not be performed. Moreover, steps in addition to orin lieu of steps 702, 704, 706, and/or 708 may be performed. Forinstance, in an example embodiment, the method of flowchart 700 furtherincludes one or more of the steps shown in flowchart 800 of FIG. 8 . Asshown in FIG. 8 , the method of flowchart 800 begins at step 802. Instep 802, coherent light is modulated in frequency to provide themodulated coherent light. In an example implementation, laser source 202modulates the coherent light 244 in frequency to provide the modulatedcoherent light.

At step 804, the modulated coherent light is split into a reference beamand a detection beam. In an example implementation, splitting optics 204split the modulated coherent light into the reference beam 246 and thedetection beam 126.

At step 806, a frequency range over which a beat frequency of a beatsignal is to be searched is reduced by more than a factor of two toenable the processing of the second measurement to determine thehigh-resolution locating information. The beat signal is an electricalresult of optical mixing of the reference beam and a reflected detectionbeam at a surface of a light detecting structure. The reflecteddetection beam results from reflection of the detection beam from thecurrent point. In an example implementation, depth measurement subsystem102 reduces the frequency range over which the beat frequency of thebeat signal is to be searched by more than a factor of two to enable theprocessing of the second measurement to determine the high-resolutionlocating information.

In another example embodiment, the method of flowchart 700 furtherincludes one or more of the steps shown in flowchart 900 of FIG. 9 . Asshown in FIG. 9 , the method of flowchart 900 begins at step 902. Instep 902, coherent light is modulated in amplitude over time to providethe modulated coherent light. In an example implementation, laser source202 modulates the coherent light 244 in amplitude over time to providethe modulated coherent light.

At step 904, a reference signal and a detection beam are formed. Thedetection beam is formed from the modulated coherent light. In anexample implementation, depth measurement subsystem 102 forms thereference signal 248A and the detection beam 126. In accordance withthis implementation, the detection beam 126 is formed from the modulatedcoherent light.

At step 906, a phase difference between the reference signal and areflected detection beam is measured. The reflected detection beamresults from reflection of the detection beam from the current point. Inan example implementation, depth measurement subsystem 102 measures aphase difference between the reference signal 248A and the reflecteddetection beam 128.

At step 908, the high-resolution locating information is determinedbased on the phase difference and the low-resolution locatinginformation. In an example implementation, depth measurement subsystem102 determines the high-resolution locating information based on thephase difference and the low-resolution locating information.

As shown in FIG. 10 , the method of flowchart 1000 begins at step 1002.In step 1002, a depth map is formed. In an example implementation,controller 108 forms the depth map 138. For instance, controller 108 mayform the depth map 138 based on a scan of a beam of laser light from thereference location 132 over points (e.g., a grid of points) in the fieldof view 130.

At step 1004, locations of objects in the depth map are interpreted. Inan example implementation, controller 108 interprets the locations ofthe objects in the depth map 138. For instance, measured distances fromthe reference location 132 to respective points in the field of view 130may indicate the locations of the objects in the depth map 138.Accordingly, controller 108 may use the measured distances to interpretthe locations of the objects in the depth map 138.

At step 1006, surfaces of the objects in the depth map are identified.For example, the surfaces of the objects may be interpreted based atleast in part on the locations of the objects. In accordance with thisexample, interpolation between points that correspond to the locationsof the objects may be performed to identify the surfaces of the objectsin the depth map. In an example implementation, controller 108identifies the surfaces of the objects in the depth map 138.

At step 1008, an image is modified in response to the locations of theobjects and the surfaces of the objects to provide a modified image. Inan example implementation, controller 108 and/or laser projectionsubsystem 106 modifies the image in response to the locations of theobjects and the surfaces of the objects to provide the modified image.

At step 1010, the modified image is projected onto one or more of thesurfaces. In an example implementation, laser projection subsystem 106projects the modified image onto the one or more surfaces. For instance,laser projection subsystem 106 may use a light redirecting element inMEMS-based scanning subsystem 104 to project the modified image onto theone or more surfaces.

In some example embodiments, one or more steps 1002, 1004, 1006, 1008,and/or 1010 of flowchart 1000 may not be performed. Moreover, steps inaddition to or in lieu of steps 1002, 1004, 1006, 1008, and/or 1010 maybe performed.

III. Example Computing System Implementation

Example embodiments, systems, components, subcomponents, devices,methods, flowcharts, steps, and/or the like described herein, includingbut not limited to flowchart 500, flowchart 600, flowchart 700,flowchart 800, flowchart 900, and flowchart 1000 may be implemented inhardware (e.g., hardware logic/electrical circuitry), or any combinationof hardware with software (computer program code configured to beexecuted in one or more processors or processing devices) and/orfirmware. The embodiments described herein, including systems,methods/processes, and/or apparatuses, may be implemented using wellknown computing devices, such as computer 1100 shown in FIG. 11 . Forexample, each of the steps of flowchart 500, each of the steps offlowchart 600, each of the steps of flowchart 700, each of the steps offlowchart 800, each of the steps of flowchart 900, and each of the stepsof flowchart 1000 may be implemented using one or more computers 1100.

Computer 1100 can be any commercially available and well knowncommunication device, processing device, and/or computer capable ofperforming the functions described herein, such as devices/computersavailable from International Business Machines®, Apple®, HP®, Dell®,Cray®, Samsung®, Nokia®, etc. Computer 1100 may be any type of computer,including a server, a desktop computer, a laptop computer, a tabletcomputer, a wearable computer such as a smart watch or a head-mountedcomputer, a personal digital assistant, a cellular telephone, etc.

Computer 1100 includes one or more processors (also called centralprocessing units, or CPUs), such as a processor 1106. Processor 1106 isconnected to a communication infrastructure 1102, such as acommunication bus. In some embodiments, processor 1106 cansimultaneously operate multiple computing threads. Computer 1100 alsoincludes a primary or main memory 1108, such as random access memory(RAM). Main memory 1108 has stored therein control logic 1124 (computersoftware), and data.

Computer 1100 also includes one or more secondary storage devices 1110.Secondary storage devices 1110 include, for example, a hard disk drive1112 and/or a removable storage device or drive 1114, as well as othertypes of storage devices, such as memory cards and memory sticks. Forinstance, computer 1100 may include an industry standard interface, sucha universal serial bus (USB) interface for interfacing with devices suchas a memory stick. Removable storage drive 1114 represents a floppy diskdrive, a magnetic tape drive, a compact disk drive, an optical storagedevice, tape backup, etc.

Removable storage drive 1114 interacts with a removable storage unit1116. Removable storage unit 1116 includes a computer useable orreadable storage medium 1118 having stored therein computer software1126 (control logic) and/or data. Removable storage unit 1116 representsa floppy disk, magnetic tape, compact disk (CD), digital versatile disc(DVD), Blu-ray disc, optical storage disk, memory stick, memory card, orany other computer data storage device. Removable storage drive 1114reads from and/or writes to removable storage unit 1116 in a well-knownmanner.

Computer 1100 also includes input/output/display devices 1104, such astouchscreens, LED and LCD displays, keyboards, pointing devices, etc.

Computer 1100 further includes a communication or network interface1120. Communication interface 1120 enables computer 1100 to communicatewith remote devices. For example, communication interface 1120 allowscomputer 1100 to communicate over communication networks or mediums 1122(representing a form of a computer useable or readable medium), such aslocal area networks (LANs), wide area networks (WANs), the Internet,etc. Network interface 1120 may interface with remote sites or networksvia wired or wireless connections. Examples of communication interface1120 include but are not limited to a modem (e.g., for 3G and/or 4Gcommunication(s)), a network interface card (e.g., an Ethernet card forWi-Fi and/or other protocols), a communication port, a Personal ComputerMemory Card International Association (PCMCIA) card, a wired or wirelessUSB port, etc. Control logic 1128 may be transmitted to and fromcomputer 1100 via the communication medium 1122.

Any apparatus or manufacture comprising a computer useable or readablemedium having control logic (software) stored therein is referred toherein as a computer program product or program storage device. Examplesof a computer program product include but are not limited to main memory1108, secondary storage devices 1110 (e.g., hard disk drive 1112), andremovable storage unit 1116. Such computer program products, havingcontrol logic stored therein that, when executed by one or more dataprocessing devices, cause such data processing devices to operate asdescribed herein, represent embodiments. For example, such computerprogram products, when executed by processor 1106, may cause processor1106 to perform any of the steps of flowchart 500 of FIG. 5 , flowchart600 of FIG. 6 , flowchart 700 of FIG. 7 , flowchart 800 of FIG. 8 ,flowchart 900 of FIG. 9 , and/or flowchart 1000 of FIG. 10 .

Devices in which embodiments may be implemented may include storage,such as storage drives, memory devices, and further types ofcomputer-readable media. Examples of such computer-readable storagemedia include a hard disk, a removable magnetic disk, a removableoptical disk, flash memory cards, digital video disks, random accessmemories (RAMs), read only memories (ROM), and the like. As used herein,the terms “computer program medium” and “computer-readable medium” areused to generally refer to media (e.g., non-transitory media) such asthe hard disk associated with a hard disk drive, a removable magneticdisk, a removable optical disk (e.g., CD ROMs, DVD ROMs, etc.), zipdisks, tapes, magnetic storage devices, optical storage devices,MEMS-based storage devices, nanotechnology-based storage devices, aswell as other media such as flash memory cards, digital video discs, RAMdevices, ROM devices, and the like. Such computer-readable storage mediamay store program modules that include computer program logic toimplement, for example, embodiments, systems, components, subcomponents,devices, methods, flowcharts, steps, and/or the like described herein(as noted above), and/or further embodiments described herein.Embodiments are directed to computer program products comprising suchlogic (e.g., in the form of program code, instructions, or software)stored on any computer useable medium. Such program code, when executedin one or more processors, causes a device to operate as describedherein.

Note that such computer-readable storage media are distinguished fromand non-overlapping with communication media (do not includecommunication media). Communication media embodies computer-readableinstructions, data structures, program modules or other data in amodulated data signal such as a carrier wave. The term “modulated datasignal” means a signal that has one or more of its characteristics setor changed in such a manner as to encode information in the signal. Byway of example, and not limitation, communication media includeswireless media such as acoustic, RF, infrared and other wireless media,as well as wired media. Embodiments are also directed to suchcommunication media.

The disclosed technologies can be put into practice using software,firmware, and/or hardware implementations other than those describedherein. Any software, firmware, and hardware implementations suitablefor performing the functions described herein can be used.

IV. Conclusion

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. It will be apparent to persons skilled in the relevant artthat various changes in form and detail can be made therein withoutdeparting from the scope of the embodiments. Thus, the scope of theembodiments should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents.

What is claimed is:
 1. A method of performing progressive resolutionrefinement, the method comprising: performing a periodic chirp in whichcoherent light is modulated in frequency over a chirp period of time toprovide modulated coherent light; modulating an emission frequency ofthe modulated coherent light to provide frequency modulation changes ina range from 150 megahertz to 150 gigahertz; performing a firstmeasurement with a relatively low resolution using the modulatedcoherent light; processing the first measurement electrically todetermine low-resolution locating information, the low-resolutionlocating information including a relatively low resolution estimate of adistance between a reference location and a current point; performing asecond measurement with a relatively high resolution; and processing thesecond measurement electrically using the low-resolution locatinginformation to enable the processing of the second measurement todetermine high-resolution locating information, the high-resolutionlocating information including a relatively high resolution estimate ofthe distance between the reference location and the current point. 2.The method of claim 1, further comprising: splitting the modulatedcoherent light into a reference beam and a detection beam; and reducinga frequency range over which a beat frequency of a beat signal is to besearched by more than a factor of two to enable the processing of thesecond measurement to determine the high-resolution locatinginformation, the beat signal being an electrical result of opticalmixing of the reference beam and a reflected detection beam at a surfaceof a light detecting structure, the reflected detection beam resultingfrom reflection of the detection beam from the current point.
 3. Themethod of claim 1, further comprising: modulating the coherent light inamplitude over time to provide amplitude-modulated coherent light;forming a reference signal and a detection beam, the detection beamformed from the amplitude-modulated coherent light; measuring a phasedifference between the reference signal and a reflected detection beam,the reflected detection beam resulting from reflection of the detectionbeam from the current point; and determining the high-resolutionlocating information based on the phase difference and thelow-resolution locating information.
 4. The method of claim 1, furthercomprising: performing a scan of the current point in an environmentusing a mirror; and forming a depth map by coordinating thehigh-resolution locating information with the scan of the current pointin the environment, wherein the depth map is a graphicalthree-dimensional representation of the environment.
 5. The method ofclaim 4, further comprising: performing laser projection by projecting atwo-dimensional image, which is based on the depth map, onto an objectin the environment.
 6. The method of claim 1, further comprising:determining Doppler velocity of a point, which corresponds to thecurrent point at a designated period of time, based on thehigh-resolution locating information.
 7. The method of claim 1, whereinthe first measurement is a measurement of another point rather than thecurrent point.
 8. The method of claim 1, further comprising: adjusting arange of frequencies over which the coherent light is modulated duringthe periodic chirp to adapt resolution of the high-resolution locatinginformation.
 9. A system to perform progressive resolution refinement,the system comprising: a laser source configured to perform a periodicchirp in which coherent light is modulated in frequency over a chirpperiod of time to provide modulated coherent light, the laser sourcefurther configured to modulate an emission frequency of the modulatedcoherent light to provide frequency modulation changes in a range from150 megahertz to 150 gigahertz; a depth measurement subsystem configuredto perform a first measurement with a relatively low resolution usingthe modulated coherent light, the depth measurement subsystem furtherconfigured to performing a second measurement with a relatively highresolution; and a signal processing circuit configured to process thefirst measurement electrically to determine low-resolution locatinginformation, the low-resolution locating information including arelatively low resolution estimate of a distance between a referencelocation and a current point, the signal processing circuit furtherconfigured to processing the second measurement electrically using thelow-resolution locating information to enable the processing of thesecond measurement to determine high-resolution locating information,the high-resolution locating information including a relatively highresolution estimate of the distance between the reference location andthe current point.
 10. The system of claim 9, further comprising:splitting optics configured to split the modulated coherent light into areference beam and a detection beam; wherein the depth measurementsubsystem is configured to reduce a frequency range over which a beatfrequency of a beat signal is to be searched by more than a factor oftwo to enable the processing of the second measurement to determine thehigh-resolution locating information, the beat signal being anelectrical result of optical mixing of the reference beam and areflected detection beam at a surface of a light detecting structure,the reflected detection beam resulting from reflection of the detectionbeam from the current point.
 11. The system of claim 9, furthercomprising: a microelectromechanical systems-based scanning subsystemconfigured to perform a scan of the current point in an environmentusing a mirror; and a controller configured to form a depth map bycoordinating the high-resolution locating information with the scan ofthe current point in the environment, wherein the depth map is agraphical three-dimensional representation of the environment.
 12. Thesystem of claim 11, further comprising: a laser projection subsystemconfigured to perform laser projection by projecting a two-dimensionalimage, which is based on the depth map, onto an object in theenvironment.
 13. The system of claim 9, further comprising: a controllerconfigured to determine Doppler velocity of a point, which correspondsto the current point at a designated period of time, based on thehigh-resolution locating information.
 14. The system of claim 9, whereinthe first measurement is a measurement of another point rather than thecurrent point.
 15. The system of claim 9, further comprising: areference fiber optic loop; and a controller configured to calibrate thedepth measurement subsystem using a measurement of a distance throughthe reference fiber optic loop, the distance through the reference fiberoptic loop being a known distance.
 16. The system of claim 9, furthercomprising: a controller configured to adjust a range of frequenciesover which the coherent light is modulated during the periodic chirp toadapt resolution of the high-resolution locating information.
 17. Amethod of performing progressive resolution refinement, the methodcomprising: modulating coherent light in frequency to provide modulatedcoherent light; splitting the modulated coherent light into a referencebeam and a detection beam; performing a first measurement with arelatively low resolution using the modulated coherent light; processingthe first measurement electrically to determine low-resolution locatinginformation, the low-resolution locating information including arelatively low resolution estimate of a distance between a referencelocation and a current point; performing a second measurement with arelatively high resolution; processing the second measurementelectrically using the low-resolution locating information to enable theprocessing of the second measurement to determine high-resolutionlocating information, the high-resolution locating information includinga relatively high resolution estimate of the distance between thereference location and the current point; and reducing a frequency rangeover which a beat frequency of a beat signal is to be searched by morethan a factor of two to enable the processing of the second measurementto determine the high-resolution locating information, the beat signalbeing an electrical result of optical mixing of the reference beam and areflected detection beam at a surface of a light detecting structure,the reflected detection beam resulting from reflection of the detectionbeam from the current point.
 18. The method of claim 17, furthercomprising: performing a scan of the current point in an environmentusing a mirror; and forming a depth map by coordinating thehigh-resolution locating information with the scan of the current pointin the environment, wherein the depth map is a graphicalthree-dimensional representation of the environment.
 19. The method ofclaim 18, further comprising: performing laser projection by projectinga two-dimensional image, which is based on the depth map, onto an objectin the environment.
 20. The method of claim 17, wherein modulating thecoherent light comprises: performing a periodic chirp in which thecoherent light is modulated in frequency over a chirp period of time toprovide the modulated coherent light; and wherein the method furthercomprises: adjusting a range of frequencies over which the coherentlight is modulated during the periodic chirp to adapt resolution of thehigh-resolution locating information.